For the testing of digital communication paths and the devices along these paths, measurement signals are used which, as a test pattern, utilize a bit sequence. The bit sequence can be a quasi-random sequence or a digital word.
At the receiver side, i.e. at the end of the path opposite that at which the test pattern is injected, a measuring device is provided which generates a reference signal with the same quasi-random sequence or with the same digital word.
The receiver measurement signal is compared with the reference signal generated at the receiver side to enable perturbations or defects along the path to be detected.
A bit-error measurement can only be carried cut with precision when the received measurement signal and the reference signal are synchronized. In the use of quasi-random sequences as test patterns in bit-error measuring devices, the so-called Gelbrich process, as described in DE-C-2359716 inhibits the new synchronization of the receiver side reference patterns even in the case of high error levels or cluster errors.
In the publication Harrison, A. F.: "Measuring Equipment for Data Transmission Channels." in: Philips Telecommunication Review Vol. 27, Aug. 1, 1967, Pages 1 to 10, a process is described which permits detection of a synchronism failure between two quasi-random sequences rather than bit sequences in the form of digital words. The synchronization of measurement signals and reference signals which are constituted as sequences of digital words (word sequences) poses a problem in that the received word sequence forming the reference pattern must also be synchronized. Individual digital words have a short periodic pulse pattern with a predetermined length which generally is between 2 and 16 bits or also between 2 and 32 bits. The pulse pattern and its length can be established at will by the device user.
For the transmitter and receiver, however, completely identical patterns must be generated to allow the reference pattern at the receiver to be used for pattern comparison with the measurement pattern.
At the beginning of a bit-error measurement, the reference pattern must be synchronized to the transmitted or captured pattern which is the measurement signal. As a criterium for new synchronization, the bit-error rate or proportion has been used heretofore. Upon exceeding a predetermined error proportion, a new synchronization of the reference pattern is initiated. With cluster errors, during which a very high error proportion can arise over a very short interval, new synchronization can be initiated which may not be necessary and the bit-error measurement can thus be interrupted or falsified.